This invention relates to an electrically powered air breathing plasma accelerator and more particularly to an electrically powered air breathing Hall effect thruster and more generally to such an electrically powered air breathing plasma accelerator, such as a Hall effect thruster, which is atmosphere breathing.
The zone between approximately 80 kilometers and 160 kilometers above the earth, known as the E region of the ionosphere, is transited only by rockets and experimental hypersonic craft with specialized propulsion such as scramjets, and their combinations with rocket engines. Conventional spacecraft must operate well above an altitude of 160 kilometers to avoid drag induced re-entry. At altitudes greater than 30 kilometers above the earth, conventional aircraft cannot operate because of the lack of lift associated with the low pressure and insufficient oxygen in the thin atmosphere to combust fuel.
Spacecraft typically employ thrusters, such as Hall effect thrusters, to generate the required thrust for on-orbit maneuvering and repositioning. These thrusters require propellant stored on-board which limits the number of times the spacecraft can be maneuvered.
A typical prior art Hall thruster includes a propellant, a discharge chamber, an externally located cathode which emits electrons, an anode, located within the discharge chamber which attracts the electrons emitted from the cathode, and an electric circuit which energizes a magnet to create a radial magnetic field and a resulting axial electric field. The magnetic field presents an impedance to the flow of electrons from the emitter to the anode. As the electrons attempt to enter the discharge chamber, the magnetic field impedes the electrons and causes them to travel in a helical fashion about the magnetic field lines. The propellant, such as xenon, is introduced through a distributor into the discharge chamber. When the electrons trapped by the magnetic field collide with the propellant (e.g., xenon) they strip electrons from the propellant, creating positively charged ions. The positively charged ions are rapidly expelled from the discharge chamber due to the axial electric field and generate thrust.
Application of a prior art Hall thruster to maintain a vehicle for extended periods of time at altitudes below and 160 kilometers above the earth, in the ionosphere, or in the atmospheres of other planets, is impractical because extensive propellant must be stored on-board the vehicle to overcome drag. Storing sufficient propellant on-board the vehicle significantly increases the weight of the vehicle which increases the thrust requirements. This increased thrust requirement results in the need for a larger and heavier thruster, which consumes more power, thus requiring larger and generally heavier power sources. This causes further increases in the atmospheric drag of a vehicle employing the thruster as an engine leading to increased thrust requirements, more propellant and more electric power than can be provided by conventional on-board power generators, thus making it impossible to maintain the vehicle at the desired altitude.
Hence, there are no practical xe2x80x9catmospheric skimmingxe2x80x9d vehicles which can operate at the high altitude of the ionosphere and the low pressure, typically much less than 1 Torr, associated with this altitude, for extended periods of time.
It is therefore an object of this invention to provide an air breathing electrically powered plasma accelerator, such as Hall effect thruster.
It is a further object of this invention to provide such an air breathing electrically powered plasma accelerator, such as Hall effect thruster, which uses air or other ambient atmospheric gas as the propellant for the thruster.
It is a further object of this invention to provide such an air breathing electrically powered plasma accelerator, such as Hall effect thruster, which operates efficiently and effectively at an atmospheric pressure of less than 1 Torr.
It is a further object of this invention to provide such an air breathing electrically powered plasma accelerator, such as Hall effect thruster, which operates efficiently and effectively in the zone below 160 kilometers above the earth.
It is a further object of this invention to provide such an air breathing electrically powered plasma accelerator, such as Hall effect thruster, which operates efficiently and effectively in the ionosphere.
It is a further object of this invention to provide such an electrically powered plasma accelerator, such as Hall effect thruster, which operates efficiently and effectively where the atmospheric pressure is less than 1 Torr in the atmosphere of any planet.
It is a further object of this invention to provide such an air breathing electrically powered plasma accelerator, such as Hall effect thruster, which reduces or eliminates the need to store propellant for the thruster on-board a vehicle employing the thruster.
It is a further object of this invention to provide such an atmospheric breathing electrically powered plasma accelerator, such as Hall effect thruster, which efficiently and effectively uses solar arrays at ionospheric altitudes where the atmospheric drag is significantly reduced, to generate the electric power required by the thruster to generate sufficient thrust to maintain a vehicle employing the thruster at such altitudes for extended periods of time.
It is a further object of this invention to provide such an atmospheric breathing electrically powered plasma accelerator, such as Hall effect thruster, which can generate thrust for greatly extended periods of time.
It is a further object of this invention to provide such an air breathing electrically powered plasma accelerator, such as a Hall effect thruster, in which the energy input is electric rather than conventional combustible fuel.
It is a further object of this invention to provide such an atmospheric breathing electrically powered plasma accelerator, such as Hall effect thruster, which utilizes atomic oxygen and naturally occurring ions located in the upper atmosphere to improve the performance of the thruster.
This invention results from the realization that a truly effective atmospheric breathing electrically powered jet engine, in the form of a unique plasma accelerator, such as a Hall effect thruster, operable at ionospheric altitudes can be achieved by using the very atmosphere in which the thruster is located as the propellant eliminating the need for storing the propellant on-board and tapping into an endless supply of propellant and by the further realization that the electrical energy required to energize the ionize and accelerate the propellant and accelerate out of the thruster to create the thrust can be obtained from an on-board solar array and which may be sufficient given the reduced drag of the altitudes to maintain vehicles at the desired altitudes for an extended period of time.
This invention features an air breathing electrically powered plasma accelerator, such as a Hall effect thruster, including a thruster duct having an inlet, an exit, and a discharge zone between the inlet and the exit for receiving air from the inlet into the discharge zone. An electrical circuit has a cathode for emitting electrons and an anode in the discharge zone for attracting the electrons from the cathode through the exit. A magnetic circuit establishes a magnetic field in the discharge zone radially across the duct between the anode and exit which creates an impedance to the flow of electrons toward the anode and enables ionization of the air moving through the discharge zone and creates an axial electric field in the duct for accelerating ionized air through the exit to create thrust.
In a preferred embodiment, the electrical circuit may include a solar array source; the electrical circuit may include a battery or fuel cell. The air breathing electrically Hall effect thruster of this invention may include a screen at the inlet for repelling electrons emitted from the cathode. The screen may include a physical conductor at or below the voltage of the cathode; the screen may include a magnetic field across the inlet. The air breathing electrically powered Hall effect thruster may operate at a pressure less than 1 Torr, or at a pressure in the range of 10xe2x88x924 to 1 Torr and altitudes in the range of 80 kilometers to 160 kilometers above the earth. In a preferred embodiment, the thruster operates in the ionosphere. The discharge zone may extend to define an increased dwell time for ionization. The discharge zone may include a plurality of magnetic circuits for establishing an extended magnetic field for increasing the dwell time.
This invention further features an atmospheric breathing electrically powered plasma accelerator, such as a Hall effect thruster, including a thruster duct having an inlet, an exit, and a discharge zone between the inlet and the exit for receiving atmospheric gas from the inlet into the discharge zone. An electrical circuit has a cathode for emitting electrons and an anode in the discharge zone for attracting the electrons from the cathode through the exit. A magnetic circuit establishes a radial magnetic field in the discharge zone across the duct between the anode and exit which creates an impedance to the flow of electrons toward the anode and enables ionization of the atmospheric gas moving through the discharge zone and creates an axial electric field in the duct for accelerating ionized atmospheric gas through the exit to create thrust.
This invention also features a high altitude low pressure electrically powered plasma accelerator, such as a Hall effect thruster, including a thruster duct having an inlet, an exit, and a discharge zone between the inlet and the exit for receiving air from the inlet into the discharge zone. An electrical circuit has a cathode for emitting electrons and an anode in the discharge zone for attracting the electrons from the cathode through the exit. A magnetic circuit establishes a magnetic field in the discharge zone across the duct between the anode and exit which creates an impedance to the flow of electrons toward the anode and enables ionization of the air moving through the discharge zone and which creates an axial electric field in the duct for accelerating ionized air through the exit to create thrust.